Water heater heating time calculator
See how many minutes the heater needs to bring the water to temperature and what that costs.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter tank volume, inlet water temperature, target temperature, heater power, efficiency and price per kwh.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Energy (kWh) = liters × 4.186 × temperature rise ÷ 3600 ÷ efficiency. Time (h) = energy ÷ heater power (kW).
Example
Inputs: Tank volume = 80 L, Inlet water temperature = 20 °C, Target temperature = 60 °C, Heater power = 2 kW, Efficiency = 95 %. Result: Heating time: 118 min; Energy used: 3.92 kWh; Cost of one full heat-up: 0.71.
Limits and caveats
- It takes water specific heat as 4.186 kJ per kg per °C and density as 1 kg per liter; both vary slightly with temperature.
- Standby heat loss from the tank after heating is not included.
Questions about this tool
How long does an 80 L heater take?
With 2 kW, from 20 to 60 °C, about 112 minutes if there are no losses.
Does a more powerful heater save energy?
No. The energy needed is the same; higher power only heats faster.
What temperature should a water heater be set to?
Many health bodies advise storing hot water at about 60 °C to limit Legionella, while taking care to avoid scalds at the tap.